From: aatd1@sgies14.sdrc.com (derek hart)
Subject: large tetras
Message-ID: <320@heimdall.sdrc.com>
Date: Fri, 8 Jan 93 16:19:00 EST
Organization: SDRC
Hi all -
Does anyone have any good suggestions for building modular tetrahedron
(triangular pyramids) box kites? I am specifically wondering about the
best design (strongest/lightest) for the interface between modules. Also,
what would be best unit size for a single module?
I seem to remember a photo of a man hanging from a very large assembly of
these kites while it was towed behind a large ship.
Thanks. Derek Hart
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From: sasaki@netop3.harvard.edu (Marty Sasaki)
Subject: Re: large tetras
Message-ID: <1993Jan11.162409.6773@das.harvard.edu>
Organization: Harvard University
Date: Mon, 11 Jan 93 11:24:09 EST
In article <320@heimdall.sdrc.com>, aatd1@sgies14.sdrc.com (derek hart) writes:
>Does anyone have any good suggestions for building modular tetrahedron
>(triangular pyramids) box kites? I am specifically wondering about the
>best design (strongest/lightest) for the interface between modules. Also,
>what would be best unit size for a single module?
One of the problems with tetras in general is that they weigh a lot
for their effective wing area. In a normal tetra it takes 6 sticks for
each cell. The tendancy is to use light materials in order to get a
kite light enough to fly in light wind.
The approach that I've seen most often is to have a large tetrahedron
frame made out of fairly strong material. Smaller tetrahedrons are
attached to this frame, sharing parts of the frame where possible.
Someone makes a tetra that uses a rather clever system of four
hollow fiberglass rods and two thin solid rods that produce a fairly
strong, yet still light weight, cell.
I've experimented with kites that use tensegrities as frames and found
that tie-wraps (those plastic things that are often used to bundle
wires together) are useful for assembling multiple sails together. You
can get tie-wraps as big and as strong as you like, they are even
being used in lieu of handcuffs.
--
Marty Sasaki Harvard University Sasaki Kite Fabrications
sasaki@netop3.harvard.edu Network Operations Division 26 Green Street
10 Ware Street Jamaica Plain, MA 02130
Cambridge, MA 02138-4002 phone/fax: 617-522-8546
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From: sgreene@access.digex.com (Stephan Greene)
Subject: Re: large tetras
Date: Sun, 10 Jan 93 13:09:33 EST
Organization: Express Access Public Access UNIX, Greenbelt, Maryland USA
Message-ID: <1ipootINNiio@mirror.digex.com>
In article <320@heimdall.sdrc.com> aatd1@sgies14.sdrc.com (derek hart) writes:
>Hi all -
>
>Does anyone have any good suggestions for building modular tetrahedron
>(triangular pyramids) box kites? I am specifically wondering about the
>best design (strongest/lightest) for the interface between modules. Also,
>what would be best unit size for a single module?
>
>I seem to remember a photo of a man hanging from a very large assembly of
>these kites while it was towed behind a large ship.
>
>Thanks. Derek Hart
Many (over fifteen!) years ago, I purchased a tetra kite kit. The joints
between "cells" were ijection modlded plastic parts with short stubs for
joining the individual cells and the stringers that formed each cell. The system
was inherently expandable, by joining groups of four-cell kites into a single
larger kite.
These joints were also rather weak, and were prone to disconnecting at
inpapprpopiate momemnts (like in flight!) and breakage on the ground.
I wonder if tinker-toy pieces and wood dowels would work? The tinker toy
pieces are rather large, but glud could keep ebexxx everything tohxxx togetger
(at the price of not being able to disassemble the monster!)
Steve Greene
sgreene@access.digex.com
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From: sc5@prism.gatech.EDU (CSEPLO,STEPHEN P)
Subject: Re: large tetras
Message-ID: <79868@hydra.gatech.EDU>
Date: Tue, 12 Jan 93 11:38:57 EST
Organization: Georgia Institute of Technology
Just one question; Why do you want to build a tetra?
If your looking for power, there are much better alternatives. If you like
the design, I would encorage you to examine the work of Bell and duplicate
his work as a historical endevor (SP?).
Otherwise, KITELINES had an article about an obtruse tetra a few issues
ago. I friend build one and it's OK, but not fantastic. The big thing
is going to be the connectors. Marty related a very valid option, the
use of wire ties. They can be had at hardware stores in the electrical
section.
--
The Mad Hata
"Hey, Mon....Tako Kichi!"
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From: jeffy@syrinx.umd.edu (Jeffrey C. Burka)
Subject: Re: large tetras
Message-ID: <17947@umd5.umd.edu>
Date: Wed, 13 Jan 93 17:15:01 EST
Organization: University of Maryland at College Park
In article <79868@hydra.gatech.EDU> sc5@prism.gatech.EDU (CSEPLO,STEPHEN P) writes:
>Otherwise, KITELINES had an article about an obtruse tetra a few issues
>ago. I friend build one and it's OK, but not fantastic. The big thing
>is going to be the connectors. Marty related a very valid option, the
>use of wire ties. They can be had at hardware stores in the electrical
>section.
I fly with Bill Kocher, the guy who wrote the article in KiteLines, and
I've seen his tetra several times. I think that if you're interested
in tetras, this really is the way to go. Admittedly, it loses a bit
in elegance and ease in building large, complex shapes, but it still
_looks_ like a tetra and it does fly in pretty low wind.
Jeff
--
|Jeffrey C. Burka | "Fairies are the perfect people to do this |
|(suffering Bad Grammar) | sort of work. Biologically, their upper |
|jeffy@syrinx.umd.edu | bodies are strong enough to wield a pickaxe...." |
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From: sc5@prism.gatech.EDU (CSEPLO,STEPHEN P)
Subject: Re: large tetras
Message-ID: <80124@hydra.gatech.EDU>
Date: Thu, 14 Jan 93 08:59:10 EST
Organization: Georgia Institute of Technology
Yeah, Jeff it does look like a tetra. But I'm trying to generate interest
in historical kites. Maybe it will get off the ground one of these days as
a comprehensive event.
When I was a kid, I built a tetra from long drinking straws and tissue
paper covering for the sail. The straws were held together by running
string through them. It flew nicely in a moderate breeze but like so
many other things from your child hood, it got destroyed when I tree'd
it and pulled it back out. Oh well.
PS: The plans were in National Geographic, circa 1967.
--
The Mad Hata
"Hey, Mon....Tako Kichi!"
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From: andrew@tug.com (Andrew Beattie)
Subject: Re: large tetras
Message-ID:
Date: Thu, 14 Jan 93 06:56:37 EST
Organization: Negligible.
In article <79868@hydra.gatech.EDU> sc5@prism.gatech.EDU (CSEPLO,STEPHEN P) writes:
>Just one question; Why do you want to build a tetra?
Don't dismiss them lightly. I'm no expert on this type of kite, but I
understand that:
1) The big ones are very stable. When a diamond kite is within a few wingspan
lengths of the ground, it becomes very unstable. This means that a big
man-lifter may be unstable while still a considerable distance off the ground.
A large matrix of Tetras tends to act as many small kites flying in formation,
multiplying the lift without sacrificing so much stability.
2) While one single cell is heavy, in a matrix, the each cell shares all
of it's sticks with adjoining cells, so the overall sail-area/weight ratio
becomes quite good.
Hmm... Perhaps I'll build a big tetra next...
Andrew
--
Andrew Beattie PO Box 109, Basingstoke, RG24 0YB, UK.
Email:andrew@tug.com Phone:+44-256-464912
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From: Peter Manson
Subject: Re: large tetras
Message-ID: <1993Jan14.144655.7179@bnr.ca>
Organization: Bell-Northern Research
X-Useragent: Nuntius v1.1.1d9
Date: Thu, 14 Jan 93 09:46:55 EST
I built a 4-cell tetra (my first) following the Kitelines article's
instructions. I found that it flies well in medium winds; say 7 - 15
km/h. If it's too windy, it rises to horizontal, the wind gets on top of
it, and it drops from the sky. I haven't tried to fix this yet; but what
I'd like to try is a two-point bridle to hold the tail end down just a
bit (the article says to just attach the flying line to the top of the
bottom edge). Will this help? Any other ideas?
As for the connectors, the method in Kitelines works quite well. The
four 3-stick joints within a cell are done with a piece of vinyl tubing
with a hole punched across the middle. (I found these to slip out
sometimes, but then I didn't paint the dowels as instructed.) The cells
are joined with a connector made out of a piece of neoprene fuel hose,
with four holes punched through it (the two top ones in the same
direction, and the two bottom ones at right angles to the top ones).
This cell-joiner is "universal": only one kind of connector is needed,
even though the different cell joints join 2, 3 or 4 cells.
The other nice thing about the design is that you can put together a
bunch of cells, and then decide on how many to assemble "in the field".
The cells can be left assembled, and stacked like chairs for transporting
them -- then all that's left to do is connect the cells.
I've got 6 more cells on the way, and maybe more after that!
Cheers.
Peter
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From: robertw@cv.hp.com (Robert B. Williams)
Subject: Re: large tetras
Message-ID: <1993Jan14.210053.21557@hpcvusn.cv.hp.com>
Date: Thu, 14 Jan 93 16:00:53 EST
Distribution: na
Organization: Hewlett-Packard Company, Corvallis, Oregon USA
I don't know much about tetra's, but I got a toy for Xmas (flexi-frame, or
something like that, not related to Flexi-Foil!) that has connectors
made of soft rubber tubing. Half the tubes have a hole punched through
the middle, in which you insert the other half of the tubes, making a 4
way connector. You then insert tinkertoy like sticks in the tubes to make
a fleixible dodacahedran or something. I'd guess surgical tubing of the
appropriate diameter would work for any kite stick. It will definitely
stick to painted spars.
Something like this:
V hole in which to insert the other tube
Half the tubes __________________________________
O
----------------------------------
The other half __________________________________
----------------------------------
Joined:
| |
| |
| |
| |
| |
________________________________
O
--------------------------------
| |
| |
| |
| |
| |
If you're having trouble getting the tube through the hole, take a short
stick, put the unholed tube on the end and use it to thread through the hole.
I suppose you could make a second hole to make n-way connectors.
--
Robert Williams robertw@hp-pcd.cv.hp.com 503-750-2818
HP in Corvallis Oregon
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Subject: Re: large tetras
Message-ID: <1993Jan14.194237.15535@stsci.edu>
From: yen@stsci.edu (Felix Yen)
Date: Thu, 14 Jan 93 14:42:37 EST
Distribution: na
Organization: Space Telescope Science Institute
The Mad Hata (sc5@prism.gatech.EDU) writes:
> Yeah, Jeff it does look like a tetra. But I'm trying to generate interest
> in historical kites. Maybe it will get off the ground one of these days as
> a comprehensive event.
>
> When I was a kid, I built a tetra from long drinking straws and tissue
> paper covering for the sail. The straws were held together by running
> string through them. It flew nicely in a moderate breeze but like so
> many other things from your child hood, it got destroyed when I tree'd
> it and pulled it back out. Oh well.
>
> PS: The plans were in National Geographic, circa 1967.
You might be interested to hear that the Smithsonian Institute marketed
a children's science kit last year that featured Alexander Graham Bell
and included a small tetra. Instead of tissue paper, some variety of
plastic. Instead of drinking straws, plastic rods. The joints are made
by tying together the centers of three lengths of plastic tubing with
plastic wire ties (the ones mentioned earlier by TMH and Marty Sasaki)
thus producing a six-way connector. It appears to be a clever design,
but the weather has prevented me from attempting a launch so far.
Felix
yen@stsci.edu
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From: sc5@prism.gatech.EDU (CSEPLO,STEPHEN P)
Subject: Re: large tetras
Message-ID: <80273@hydra.gatech.EDU>
Date: Fri, 15 Jan 93 08:53:29 EST
Distribution: na
Organization: Georgia Institute of Technology
In article <1993Jan14.194237.15535@stsci.edu> yen@stsci.edu (Felix Yen) writes:
(edited)
>The joints are made
>by tying together the centers of three lengths of plastic tubing with
>plastic wire ties (the ones mentioned earlier by TMH and Marty Sasaki)
>thus producing a six-way connector. It appears to be a clever design,
>but the weather has prevented me from attempting a launch so far.
That does sound clever. Thanks for mentioning it.
--
The Mad Hata
"Hey, Mon....Tako Kichi!"
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